Peripheral blood leukocytes (PBL) were drawn from a number of age matched heterosexual and homosexual men from the Washington, D.C. area, and New Mexico. The PBL were sensitized in vitro to influenza virus and to HLA alloantigens. These sensitized cultures were tested for the generation of cytotoxic T lymphocytes (CTL) specific for influenza virus and alloantigens. Assays were also run for OKT4:OKT8 ratios (i.e., helper:suppressor cell), and for interferon production in culture in the presence of influenza virus. In the Washington group, anti-influenza CTL responses were reduced in approximately 25% of the donors except one exhibited normal OKT4:OKT8 and thymosin Alpha 1 levels. Heterosexuals generated CTL responses within the normal range to influenza virus. Approximately 40% of the New Mexico homosexual donors without any detectable loss in reactivity to HLA alloantigens. Abnormalities were also detected in interferon in this group, although all of these donors exhibited elevated CTL activity to HLA alloantigens without any reduction in CTL to influenza. The one donor from the Washington group that had a OKT4:OKT8 reversal and that exhibited no CTL to influenza developed AIDS after 10 months in our study. His sera had antibody activity to HTLV-III and cultures of his lymphocytes exhibited elevated levels of reverse transcript activity.